Support active connect, overwrite log

Added options:
  --switch-ip   If set, actively connect to this switch on controller-port
  --log-append  Append to existing log

The default log file generation behavior has changed.  By default, now
over-write the existing log.  To have the old append behavior, use the
--log-append option.

Active switch connections have been tested, but not exhaustively.  It
shold still be considered experimental.  The old behavior (listen for
switch connections) should be unchanged.
3 files changed